Why is the sun the brightest star?

Answer 1

The Sun isn't the brightest star, actually it's considered quite dim in relation to other stars.
It appears brightest as it is closer to earth. There are other stars, some bigger or smaller, brighter or duller, in the vastness of the universe outside our rather small collection of planets orbiting our sun.

Answer 2

It appears the brightest because it is comparatively close to us. It is a rather average star.